A Better Index of Body Adiposity
Total Page：16
File Type：pdf, Size：1020Kb
University of Pennsylvania ScholarlyCommons Departmental Papers (Vet) School of Veterinary Medicine 5-2011 A Better Index of Body Adiposity Richard N. Bergman Darko Stefanovski University of Pennsylvania, [email protected] Thomas A. Buchanan Anne E. Sumner James C. Reynolds See next page for additional authors Follow this and additional works at: https://repository.upenn.edu/vet_papers Part of the Disease Modeling Commons Recommended Citation Bergman, R. N., Stefanovski, D., Buchanan, T. A., Sumner, A. E., Reynolds, J. C., Sebring, N. G., Xiang, A. H., & Watanabe, R. M. (2011). A Better Index of Body Adiposity. Obesity: A Research Journal, 19 (5), 1083-1089. http://dx.doi.org/10.1038/oby.2011.38 At the time of publication, author Darko Stefanovski was affiliated with theeck K School of Medicine at the University of Southern California. Currently, he is a faculty member at the University of Pennsylvania's School of Veterinary Medicine. This paper is posted at ScholarlyCommons. https://repository.upenn.edu/vet_papers/137 For more information, please contact [email protected]. A Better Index of Body Adiposity Abstract Obesity is a growing problem in the United States and throughout the world. It is a risk factor for many chronic diseases. The BMI has been used to assess body fat for almost 200 years. BMI is known to be of limited accuracy, and is different for males and females with similar %body adiposity. Here, we define an alternative parameter, the body adiposity index (BAI = ((hip circumference)/((height)1.5)–18)). The BAI can be used to reflect %body fat for adult men and women of differing ethnicities without numerical correction. We used a population study, the “BetaGene” study, to develop the new index of body adiposity. %Body fat, as measured by the dual-energy X-ray absorptiometry (DXA), was used as a “gold standard” for validation. Hip circumference (R = 0.602) and height (R = −0.524) are strongly correlated with %body fat and therefore chosen as principal anthropometric measures on which we base BAI. The BAI measure was validated in the “Triglyceride and Cardiovascular Risk in African-Americans (TARA)” study of African Americans. Correlation between DXA-derived %adiposity and the BAI was R = 0.85 for TARA with a concordance of C_b = 0.95. BAI can be measured without weighing, which may render it useful in settings where measuring accurate body weight is problematic. In summary, we have defined a new parameter, the BAI, which can be calculated from hip circumference and height only. It can be used in the clinical setting even in remote locations with very limited access to reliable scales. The BAI estimates %adiposity directly. Disciplines Disease Modeling Comments At the time of publication, author Darko Stefanovski was affiliated with theeck K School of Medicine at the University of Southern California. Currently, he is a faculty member at the University of Pennsylvania's School of Veterinary Medicine. Author(s) Richard N. Bergman, Darko Stefanovski, Thomas A. Buchanan, Anne E. Sumner, James C. Reynolds, Nancy G. Sebring, Anny H. Xiang, and Richard M. Watanabe This journal article is available at ScholarlyCommons: https://repository.upenn.edu/vet_papers/137 A Better Index of Body Adiposity Richard N. Bergman1, Darko Stefanovski1, Thomas A. Buchanan2,3, Anne E. Sumner4, James C. Reynolds5, Nancy G. Sebring6, Anny H. Xiang7, and Richard M. Watanabe8 1Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, USA 2Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, USA 3Department of Ob/Gyn and Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, USA 4Clinical and Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Disease (NIDDK), National Institutes of Health, Bethesda, Maryland, USA 5Department of Radiology and Imaging Sciences, Nuclear Medicine, National Institutes of Health, Bethesda, Maryland, USA 6Nutrition, National Institutes of Health, Bethesda, Maryland, USA 7Department of Research and Evaluation, Kaiser Permanente Southern California Medical Group, Pasadena, California, USA 8Department of Preventive Medicine, Division of Biostatistics, Keck School of Medicine, University of Southern California, Los Angeles, California, USA Abstract Obesity is a growing problem in the United States and throughout the world. It is a risk factor for many chronic diseases. The BMI has been used to assess body fat for almost 200 years. BMI is known to be of limited accuracy, and is different for males and females with similar %body adiposity. Here, we define an alternative parameter, the body adiposity index (BAI = ((hip circumference)/((height)1.5) − 18)). The BAI can be used to reflect %body fat for adult men and women of differing ethnicities without numerical correction. We used a population study, the “BetaGene” study, to develop the new index of body adiposity. %Body fat, as measured by the dual-energy X-ray absorptiometry (DXA), was used as a “gold standard” for validation. Hip circumference (R = 0.602) and height (R = −0.524) are strongly correlated with %body fat and therefore chosen as principal anthropometric measures on which we base BAI. The BAI measure was validated in the “Triglyceride and Cardiovascular Risk in African-Americans (TARA)” study of African Americans. Correlation between DXA-derived %adiposity and the BAI was R = 0.85 for TARA with a concordance of C_b = 0.95. BAI can be measured without weighing, which may render it useful in settings where measuring accurate body weight is problematic. In summary, we have defined a new parameter, the BAI, which can be calculated from hip circumference and height only. It can be used in the clinical setting even in remote locations with very limited access to reliable scales. The BAI estimates %adiposity directly. Bergman et al. Page 2 INTRODUCTION Alarming increases in adiposity have been identified in the United States and in other affluent countries (1–3). Obesity is a risk factor for many diseases, including type 2 diabetes mellitus, cardiovascular disease, hypertension, and cancer (4,5). Worldwide increases in diabetes and other chronic diseases will cause great suffering, and overwhelm medical treatment systems. Thus, there have been heroic efforts to attempt to reverse the increase in obesity, although such reversal has proved intractable in many situations (6). It is important to target efforts to reduce adiposity for groups most at-risk for obesity-related chronic diseases. Various methods have been developed to assess adiposity. Underwater weighing and dual-energy X-ray absorption (DXA) are most accurate for quantifying body fat, and computed tomography scans and magnetic resonance imaging can assess body fat distribution. However, such technologically complex methods are too costly and time consuming to be applied routinely in clinical settings. Surrogate methods such as impedance analysis and skin-fold thickness can also be used, but are notoriously inaccurate (7,8). Other than simple measurement of body weight, the BMI is by far the most commonly applied approach to characterize obesity in individual subjects. This measure was introduced in the 19th century by Quetelet (9), who recognized that it is necessary to correct for differences in body size when comparing adiposity among patients. Because growth is linear, weight cannot increase as the cube of height, but as the square, and the human represents a cylinder more than a sphere. Quetelet’s index, renamed the BMI by Ancel Keys (10), is the ratio of weight to height squared. The BMI is now routinely applied to estimate body fat, not only in epidemiological studies, but also in clinical practice, despite warnings that it is not a very accurate measure of adiposity in individual patients (11). The BMI is particularly inaccurate in subjects with elevated lean body mass, such as athletes, and cannot be generalized among different ethnic groups (12,13). It is likely that individuals are often misdiagnosed as having inappropriate body fat due to variation in muscle mass, and that certain subjects with significant adiposity are overlooked. Determining adiposity in children is particularly difficult. In children, the most prevalent approach of determining body composition is to use BMI normalized by age (14). This in turn leads to complex mathematical calculations which require access to calculation software or the use of charts and tables which may not be available to those working in the health and nutrition field. Large cohorts are required to estimate the normalization factors that later are to be used by the practitioners. Furthermore, the BMI cannot be calculated in settings where accurate measures of body weight cannot be obtained (e.g., in fieldwork or in underdeveloped countries). METHODS AND PROCEDURES Identification of the index: The BetaGene study To define a measure of adiposity we initially queried a single, large study in which a variety of body measures were made. The “BetaGene” study was performed by three of the coauthors (T.A.B., R.M.W., and A.H.X.). Recruitment has been described in detail previously (15). Briefly, 1,733 subjects are Mexican American (Table 1, both parents and ≥3 grandparents Mexican or of Mexican descent) who are either probands with gestational diabetes mellitus (GDM) diagnosed within the previous 5 years (16) and their siblings and cousins, or probands with normal glucose levels in pregnancy in the past 5 years. All probands were identified from the patient populations at Los Angeles County/USC Medical Center, the Kaiser Permanente Southern California health plan membership, and OB/GYN clinics at local hospitals in Los Angeles. GDM probands were required to have glucose levels associated with poor pancreatic β-cell function and a high risk of diabetes when not Obesity (Silver Spring). Author manuscript; available in PMC 2012 February 8. Bergman et al. Page 3 pregnant (17), have no evidence of β-cell autoimmunity by GAD-65 testing, and have at least two siblings available for study.